We are studying the heart to gather new information regarding how the heart functions as a pump. We hope to learn how the pumping ability of the heart is maintained in health and disease. Patients selected are scheduled for a routine heart catheterization to determine the severity of their heart valve problem. Patients who participate will undergo additional studies after the completion of the routine heart catheterization which demonstrated no blockages in the coronary arteries. These additional studies will include: 1) placement of a temporary heart pacemaker, 2) placement of a special pressure sensing catheter into the heart, 3) placement of a catheter into the coronary sinus, 4) infusion of 3H-norepinephrine, 5) multiple blood samples (a total of not more than 150 ccs, or 3 tablespoons), 6) an injection into your vein of technetium-99m with drugs to increase or decrease your blood pressure (methoxamine or nitroprusside), 7) a dobutamine echocardiogram, 8) a blood test to measure the cytokine and catecholamine levels in your blood, and 9) heart muscle biopsies. A more complete explanation follows.A temporary pacing wire will be used to keep your heart rate constant during the study. A special catheter will be inserted into the major pumping chamber of your heart to measure precise pressure in it. A catheter will also be inserted through a small, flexible catheter into the vein (coronary sinus) that drains blood from your heart to measure the blood flow to your heart. The study procedure will involve infusion by vein of a radioisotope (3H-norepinephrine) that will be maintained for 60 minutes.Multiple blood samples will be drawn from the sheath in the artery in your leg and from the catheter in the vein that drains the blood from your heart at specific times during the infusion and for 20 minutes following completion of the infusion to measure the activity of the sympathetic nervous system both in the whole body and the heart. Then, your heart will be paced at 100 beats per minute. Measurement of precise pressures in the pumping chamber and movies of your heart will be acquired using another radioisotope (technetium-99m) injected by vein both at rest and with drugs to increase or decrease your blood pressure (methoxamine or nitroprusside) within a range that it might vary normally during the day. It is estimated that 150 minutes will be required for the additional portion of the heart catheterization to be completed. On a separate day, a dobutamine echocardiogram will be done. This test uses sound waves to create moving pictures of the heart. Pictures of the heart will be taken at rest and while a medication, dobutamine, is infused into a vein. This test allows us to see how the heart muscle and heart valves are working at rest and under periods of stress or exertion. All women of child bearing potential will have a pregnancy test before any study clinic visits. If there is a severe leak of the mitral valve and heart valve surgery is needed, patients will be referred for surgical procedure to repair the mitral valve. This is the optimal surgical procedure for this heart valve problem. During the operation, small biopsy specimens of the heart muscle will be taken to determine whether any structural change or damage to the heart muscle has occurred as a result of the heart problem. We would like to follow the patients who do undergo surgery to repair their mitral valve during the first year of recovery. This would involve an echocardiogram and MUGA scan approximately three and twelve months after surgery and clinic visits to assess each patients health status.